This report evaluates current knowledge of the mechanisms of activation/detoxication of DNA damaging agents, organotropic and cell-structure effects, induction and repair of DNA damage, and the molecular and phenotypical analysis of mutation induction This evaluation is presented in seven contributed papers and a joint report which was prepared at a workshop held at the National Institute of Environmental Health Sciences (NIEHS), Research Triangle Park, North Carolina, USA in March 1990. The joint report includes general recommendations aimed at improving research in this field and developing methodologies for genotoxicity testing, taking account of the potentials and limitations of available animal models.